1. Field of the Invention
The present invention relates to a transmission control system having a shift actuator and a select actuator to control the transmission and the clutch according to the amount of pressdown of the accelerator pedal and the vehicle speed.
2. Description of the Prior Art
FIG. 3 shows a conventional transmission control system which includes a parallel axis gear type transmission 1; an actuator 2 consisting of a select actuator 2a and a shift actuator 2b to control the transmission I for making a gear shift. Both of the actuators 2a and 2b are driven by a hydraulic drive system 3 which consists of a tank 3a, a pump 3b, and an accumulator 3c. The driving gear of the transmission 1 is controlled by a pair of piston rods 2c and 2d. This control is made by the drive unit 2e, which in turn is controlled by the main control unit 4. A pair of potentiometers 2f and 2g are provided to detect the positions of the piston rods 2c and 2d. The drive unit 2e performs a feedback control so that the actual position signals from the potentiometers 2f and 2g match the target position signal M from the main control unit 4. Consequently, the shift lever 50 drives shift blocks 51-53 to make a gear shift from the neutral "N" to the first gear "1", second gear "2", third gear "3", fourth gear "4", fifth gear "5", or reverse "R" as shown in FIG. 5(a).
A clutch 6 is linked to the piston rod 7a of a clutch actuator 7 for making connection or disconnection. The hydraulic pressure is supplied to the clutch actuator 7 from the hydraulic drive system 3 to make a feedback control by the drive unit 7b so that the actual position signal of the piston rod 7a matches the target position signal C from the main control unit 4. The drive unit 7b is controlled by the main control unit 4. An engine 8 has a control unit 9 which is controlled by the main control unit 4. The rotation of the engine 8 is transmitted to an axle 10 via the clutch 6 and the transmission 1.
The main control unit 4 receives signals from an accelerator pedal sensor 11, a brake pedal sensor 12, a key switch 13, an exhaust brake switch 14, and a selector 15 and a rpm output signal W from a vehicle speed detector 22 which is mounted on an output shaft 1a and controls the drive units 2e and 7b, the control unit 9, a display panel 16, and a control unit 17a which controls a gear position display panel 17. The main control unit 4 multiplies the rpm output signal W from the vehicle speed detector 22 by a constant .alpha. which consists of the radius r of wheels 23 and the gear ratio of a differential gear 24 to provide a vehicle speed V. Thus, the main control unit 4 controls the clutch 6 and the transmission 1 in response to the amount of pressdown of the accelerator pedal, the vehicle speed, and the shift position of the selector 15. The fourth and fifth gears "4" and "5" of the selector 15 are automatic transmission modes between first and fourth gears, and second and fifth gears, respectively.
As FIG. 4 shows, the transmission 1 has a synchromesh mechanism le consisting of a synchronizer hub 1f and a cone clutch 1c for preventing gear noise upon gear shift. The synchronizer hub 1f of a sleeve 1d rotatably and slidably mounted on the shaft 1a is pressed to the cone clutch 1c of a gear 1b so that the shaft la and the gear 1b are synchronized and connected.
As FIG. 5(a) shows, a gear shift is made by moving the shift lever 50 to the select position with the select actuator 2a and then shifting one of the shift blocks 51-53 in the shift direction with the shift actuator 2b. At this point, the dog clutch 1d is slidably moved on the shaft 1a by the actuators 2a and 2b for engagement with the gear 1b. When the gear 1b and the shaft 1a are connected, the driving power is transmitted via another gear 1m and shaft 1n.
As FIG. 5(b) shows, however, the shift lever 50 can be stuck between the shift blocks 52 and 53, for instance, or the actuator 2a and/or 2b can simply malfunction, failing to make a gear shift. In order to detect this gear shift failure, a variety of measures have been proposed in Japanese Patent Application Kokai Nos. 60-11759, 60-222328, 62-278342, 62-278343, and 62-288755. All of these measures detect the gear shift failure based on the time elapsed since the gear shift operation is started so that it has been impossible to detect the failing conditions such as the position of the failed actuator 2a or 2b. Thus, it has been difficult to provide an appropriate countermeasure. Then, Japanese Patent Application Kokai No. 62-288756 has proposed to detect the operational speed of the actuator to determine that the actuator is faulted when the operational speed is low for a predetermined time and stop the shift operation to the target gear so that the gear shift can be repeated later.
In the above conventional transmission control system, however, the transmission 1 is equipped with the synchromesh mechanism 1e so that the operational speed of the actuator 2b is reduced in the operational range of the synchromesh mechanism 1e with the friction produced by the engagement between the synchronizer hub and the gear. This reduction in the operational speed has often been mistaken as a gear shift failure.